The invention relates to a switchable coupling, particularly for auxiliary assemblies in passenger cars, having an electrically, mechanically, pneumatically or hydraulically actuated activation system, between a drive element, for example structured as a pulley, and a power take-off element, wherein the activation system comprises a switching member that can be moved, when the activation system is actuated, counter to the force of one or more reset elements, such as springs, for example, between a switching start position and a switching end position, wherein the switching member, in the switching end position, produces an operative connection between the drive element and the power take-off element, so that when the drive element is rotating, the power take-off element and an auxiliary coupling connected with the power take-off element are put into rotational motion, wherein after de-actuation of the activation system, the locking elements situated on the auxiliary coupling produce an operative connection between the drive element and the power take-off element by friction fit and/or shape fit, so that even after de-actuation of the activation system, a torque can be passed from the drive element to the power take-off element, wherein the operative connection is only interrupted when the speed of rotation of the drive element drops below a limit value.
Similar couplings are used, for example in passenger cars, for turning on auxiliary assemblies, such as, for example, a coolant compressor, and are driven by the internal combustion engine by way of a belt drive. In order to separate the auxiliary assemblies from the belt drive when they are not in use, and thereby to save drive energy, switchable couplings, as described in European patent document EP 1378 677 A2, for example, are used. These couplings are switched using an electrically activated magnetic coil. They have the disadvantage that at least in one switching position for the switching state “coupling=closed” or the switching state “coupling=open,” the electrically actuated activation system must have current applied to it permanently, and thereby it consumes energy, because in the switched state of the magnetic coil, electrical power must be permanently applied, and this leads to increased fuel consumption in the case of a passenger car.
In German patent document DE 637 795 A, a coupling is described that comprises an activation system with which a friction coupling can in turn be switched. Using this friction coupling, a connection is produced between a drive element and a power take-off element. An auxiliary coupling connected with the power take-off element has movable centrifugal weights, which produce a force-fit operative connection between the drive element and the power take-off element starting from a specific speed of rotation of the power take-off element, as a result of the centrifugal forces in effect, so that a torque can be transferred from the drive element to the power take-off element. As soon as this operative connection has been produced, the friction coupling can be released. The disadvantage of this coupling now consists in that no device with which the centrifugal weights can be reliably brought out of the operative connection between the drive element and the power take-off element, below a specific speed of rotation or when shutting off the coupling, is provided. Furthermore, no shape-fit torque transfer is described in this coupling, and therefore the ability to transfer high torques, while simultaneously requiring little construction space, is not guaranteed. Furthermore, at low speeds of rotation and the low centrifugal forces connected with this, the case can occur that the friction forces in the operative connection are not sufficient to reliably transfer the required power take-off torque. Because, in the case of this solution, an operative connection between the drive element and the power take-off element can be produced, using the centrifugal weights, even when the drive element and the power take-off element have greatly different speeds of rotation, a shock and therefore great component stresses can be caused at that moment when the centrifugal bodies enter into the operative connection.
From documents DE 619 879 A (Germany), U.S. Pat. No. 5,014,841 A (United States), DE 34 27 091 A1 (Germany), WO 2008/014 294 A2 (International), and DE 25 15351 C2 (Germany), couplings are known in which clamping elements or activation organs that can be radially activated are structured as rotationally movable clamping bodies and can be moved out counter to the spring force of a spring, wherein the clamping elements or activation organs in these couplings are structured exclusively as auxiliary organs and do not serve directly for transfer of the torque.
In German patent documents DE 10 2008 031 527 A1 and DE 29 17 448 A1, centrifugal force couplings are described, which have centrifugal weights that can be pivoted into a switching position in which they engage. The disadvantage of these couplings consists in that the centrifugal weights move exclusively on the basis of the engaging centrifugal forces, because no auxiliary devices are provided on the couplings, with which devices turning them on or off can be influenced.
The invention is therefore based on the task of developing a switchable coupling, particularly with an electrically, mechanically, pneumatically or hydraulically actuated activation system, in which the activation system has electrical power applied to it or must be mechanically actuated or activated with pneumatic or hydraulic pressure only during the closing and opening process, because the switchable coupling afterwards holds itself in the decisive switching positions for the switching states “coupling=closed” and “coupling=open” on the basis of its structure, and therefore power is not permanently required, neither in the open nor in the closed state. Furthermore, in the case of the coupling according to the invention, the torque is supposed to be reliably transferred from the drive element to the power take-off element in the state “coupling=closed.” Furthermore, the operative connection between the drive element and the power take-off element is supposed to be reliably interrupted (“coupling=open”), using a reset element, as soon as the speed of rotation of the drive element drops below a specific limit value. Furthermore, no shocks or impermissibly high component stresses should occur during switching of the coupling.
This task is accomplished, according to the invention, by a coupling having an electrically, mechanically, pneumatically or hydraulically actuated activation system, which has a switching member that stands in connection with the power take-off element, which member can be moved, by actuation of the activation system, between a switching start position and a switching end position, counter to the force of one or more energy-storing reset elements, such as reset springs, for example, from the switching start position to the switching end position.
If, for example, the activation element is configured in the form of an electromagnet, movement of the switching member counter to the force of the reset element takes place when the magnet is actuated, from the switching start position to the switching end position. After de-actuation of the activation element, the switching member is moved from the switching end position to the switching start position, by the force of the reset element.
Furthermore, the coupling according to the invention has an auxiliary coupling that has a flange that stands in connection with the power take-off element. This flange in turn stands in connection with the switching element, in such a manner that a torque can be passed from the drive element, by way of the switching member, to the power take-off element. By the actuation of the activation system, the switching member is moved from the switching start position to the switching end position, counter to the force of one or more reset elements. In the switching end position, a first friction surface situated on the switching member comes into a friction-fit operative connection with a second friction surface disposed on the power take-off element, so that the power take-off element can be driven. Furthermore, one or more holding bolts and/or guides are disposed on the flange, where a locking body sits on each holding bolt or in each guide, so that it can be moved by rotation and/or displacement, and the movement of each locking body is limited, in one direction, by at least one stop on the flange. Furthermore, one or more resilient reset elements are disposed on the flange, which elements press the locking bodies against their stops. The locking bodies and the resilient reset element are structured in such a manner that starting from a specific speed of rotation of the power take-off element, the locking bodies lift off from the stop as the result of the acceleration forces that are in effect, and move counter to the force of one or more reset elements. After de-actuation of the activation system, these locking bodies get into a friction-fit and/or shape-fit operative connection with the drive element, where this operative connection is maintained even after de-actuation of the activation system and the resulting reset of the switching member from the switching end position. From this, the advantage results that without further introduction of energy into the activation element, the switching state “coupling=closed” is maintained, and therefore the torque is reliably transferred from the drive element to the power take-off element, by way of the auxiliary coupling, specifically until the speed of rotation of the drive element and therefore of the power take-off element drops to such an extent that the locking bodies move out of the operative connection with the drive element as the result of the reset force of the reset elements. Under specific conditions, such as, for example, a short time after actuation of the activation system, the case can occur that a significant difference in the speed of rotation is present between the drive element and the power take-off element. This difference in the speed of rotation can lead to the result that a shock occurs at the moment of contact between the locking bodies and the drive element, resulting in very great component stresses. In order to prevent this, each locking body has a first operative surface that comes into contact with a second operative surface, which is situated either on the switching member or on the drive element, when the switching member moves in the direction of the switching end position, so that movement of the locking body about the holding bolt or along the guide groove is avoided, and thereby shock-like unlocking of the locking bodies is prevented.
If the activation system is actuated for a defined period of time, it can be ensured that only a slight difference in speed of rotation between the drive element and the power take-off element is present. Afterward, the switching member is moved in the direction of the switching start position as the result of de-actuation of the activation element, by the force of one or more reset elements. As a result, the two stated operative surfaces on the locking body and on the switching member or the drive element come out of contact, and therefore the locking bodies are able to move about the holding bolt or along the guide groove. Because of the acceleration forces that are in effect, the locking bodies then ultimately get into a friction-fit and/or shape-fit operative connection with the drive element, counter to the force of one or more reset elements, at a minimal difference in speed of rotation, and the torque is therefore transferred from the drive element to the power take-off element, by way of the auxiliary coupling.
Preferably, the resilient reset elements engage on the locking bodies in such a manner that they bring them out of engagement with the drive element below a specific speed of rotation of the power take-off element, even counter to a residual clamping moment.
The advantage of this invention consists in that the activation system no longer has to have electrical current applied to it, to be mechanically activated or to have hydraulic or pneumatic pressure applied to it, after the connection between the drive element and the power take-off element has been produced by the locking bodies. Therefore energy can be saved. Furthermore, this solution is characterized, above all, by a small construction space and low weight.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.